Conventional modern sail cloth is made from synthetic polymer yarns that are woven together in a typical fashion. In a weaving operation, a plurality of continuous yarns, called "warp" yarns, are arranged in parallel in the machine direction. A plurality of fill or weft yarns are successively passed over and under the warp yarns in a direction perpendicular to the warp yarns in order to produce a woven textile. The number of yarns or counts per inch may be varied in either direction to provide varying properties in the final cloth, and the weight of the yarns also contributes to the weight per unit area of the resulting cloth.
Conventional sails have typically been made from cloth having a so-called plain weave, in which single warp and fill yarns intersect to form a regular matrix. The final properties of the cloth have been controlled primarily by altering the counts of the respective warp and fill yarns per lineal inch and by selection of various sizes of yarns.
Some primary properties or qualities to be considered in sail cloth are stretch resistance, tensile strength and tear resistance in both the warp and fill directions. Additional qualities include diagonal stretch resistance, porosity, and flexibility for purposes of folding. In many cases, if an attempt is made to maximize certain desired properties, other properties will suffer considerably.
As an example of the foregoing, spinnaker cloth is made from plain woven nylon yarns, with the warp yarns being arranged substantially in parallel with the direction of maximum load on the sail. In order to provide adequate strength in the warp direction, it has been proposed to increase the count of warp yarns relative to the count of the fill yarns. While this measure does in fact increase warp strength, the warp tear resistance is significantly reduced. This is presumably, due to the tight packing of the warp yarns in the weave, which decreases the mobility of such yarns. The less mobile yarns cannot move, bunch up or realign themselves sufficiently under conditions of tear and are therefore are more prone to individual rupture and tear failure.
In connection with other types of sail cloths, it may be desirable to increase either tear or stretch resistance in areas of high stress on the cloth without excessive compromise to the other properties, and in many cases, it would be impossible or impractical to do so with conventional plain woven cloths.